Posted
by
samzenpus
on Monday November 28, 2011 @09:30AM
from the wandering-eyes dept.

ryzvonusef writes "Instructables Member 'Dimovi' utilized a spare LCD monitor and converted it into a 'privacy' monitor. He took apart the monitor's plastic frame, cutting out the polarized film with a utility knife and removed the film adhesive from the glass panel before reassembling the monitor, which now shines a bright white regardless of what is actually being displayed on the screen. He then removed the lenses from a pair of theater 3D glasses, and replaced it with the polarized film he had just removed from the monitor. Now, he is the only one who can see what he is doing on his computer."

Which laws do apply during flight depends...on many things, but the general rule is that while in flight the laws of the country of registration of the plane apply. For commercial flight not registered in the same country as the commercial operator of the flight, the operator country's laws do apply. This matters for what happens between the passengers inside the plane.

The above statement is, obviously, overly simplified, since many things can complicate matters. For example the flight could be leased in a

You *do* know that a lot of sunglasses contain polarisers, so your neighbour on the plane might get the action as well? Observe what happens with some monitors viewed through sunglasses when you've got the monitor in portrait, others seem to have it twisted 45degrees so as not to black it out whichever way it is.

In theory, yes. All he's done is removed the static polarizing filter from the display, and placed it in his glasses. As such, he needs to be precisely aligned to get proper color reproduction, Anyone else similarly aligned can see exactly what he sees. Alternatively, for a good time, take LSD and spin the monitor.

Before you do something stupid, know that there's polarizing filters for DSLR cameras, so not only would you risk being seen by people with polarizing glasses, you'd risk being photographed watching midget porn in public too. And in the picture it would look like you're doing it in a totally shameless manner too, not through invisible glasses.

It helps significantly if you have the assembly manual but not required.

I won't disassemble or reassemble any laptop that wasn't my own, for love nor money, unless I've got a manual... which pretty much limits that to Dell machines (LOVE their documentation online) or Apple computers (due solely to the existence of iFixit), but that's just IME, of course.

Granted, when I first attempted tearing apart and repairing laptops (It's a computer, how hard could it be!), I either was unable to fix them, or ended up making the problem worse, or ended up with "extra" screws, or whatever.

Pal, I do maintenance. Big stuff, small stuff, and everything in between. Electronics, hydraulics, electrical, heating, cooling, servo motors - you name it. If we take something apart, and put it back together, and we DO NOT HAVE any left over parts, we know that we've screwed up.

Once in awhile, we have to open the patient back up, to put one or more of those spare parts where it belongs, but that doesn't happen very often.

HP are pretty good with this kind of information now, too (and not just for laptops). There's a wealth of information and videos in their 'Customer Self Repair' section online here: http://h20464.www2.hp.com/index.html [hp.com]

Umm... have you actually disassembled an Laptops LCD screen?after taking the actual display out of the case, don't be fooled by thinking that thin == simple.There are about 7 separate paged layers sandwiched into metal bezel... not actually hard to deal with, but if you dislodge one, you can destroy your screen (all the electronic connections are from 1 edge of the screen - the top, when I did it).Putting it back together was a bit difficult... the backlight shines up through the screen, and it took me a dozen tries to get it to the point where the screen was usable.

It was a very fiddly job overall.... especially when in the end it was so easy to resolder the CCL that was attached to the bezel (I didn't need to dissassemble the display at all)...

Mind you, the laptop in question is the better part of 10 years old, so you have an easier time of it.

Cool and clever hack. But it assumes that what you're displaying on the screen is more embarrassing than being seen wearing 3D glasses. An easier solution would be to just never let anyone into your lair.

Cool and clever hack. But it assumes that what you're displaying on the screen is more embarrassing than being seen wearing 3D glasses. An easier solution would be to just never let anyone into your lair.But then you'd have to hoover the Cheeto crumbs from under your Command Throne yourself.

You can put the film on any pair of shades. All it requires is a linearly polarized filter. Unfortunately, you'll find a wide selection of sunglasses with linearly polazized lenses (advertised as reducing reflections) at your local gas station. Although, they might be 90 degrees off.

i don't get why he used 3d glasses. he could have gotten demo glasses (with the non refracting lenses) and added the film to them instead. then they would have just looked like sunglasses, instead of bluetard 3D glasses.

Yup. What you need is to hack one of the 3D systems that uses active LCD shutter glasses.

The screen would rapidly alternate between showing the actual image and a screen full of dazzling random hash. The shutter glasses, synced to the monitor would block out the hash and allow the user to see the image. Use a sync cable rather than some optical system, let the frequency wander randomly a bit and include some rogue flickering with the hash to make it hard for a bystander with active glasses to get in sync

If you're wearing a pair of polarized sunglasses, it's always good for a couple seconds of entertainment to sit there and look like an idiot tilting your head back and forth watching an LCD screen flip back and forth between normal and all black as the polarization lines up / goes perpendicular to the monitor's.

I suggested something similar to improve the contrast in the sonar room on submarines, without tripping up the people who were doing other things. Polarize the displays up and down, and the room lights side to side. People wearing polarized glasses could see the displays well, but the glare from the room lights would be diminished.

I think the first description of such a system was in a golden age science fiction story. Car head lights were polarized diagonally. You'd wear glasses that allowed your light to be bright, but oncoming ca's headlights would be reduced. Of course unsuspecting pedestrians would be blinded.

Privacy filters prevent viewing the screen from other than directly in front of it. This solution means nobody can see what's on the screen at all unless they wear the glasses. It just looks like a blank white page with a lightbulb behind it.

This glasses-based solution seems much more effective, especially for those who already wear glasses. Adding a polarised coating would cost pennies.

But hardly a security feature... merely a privacy screen with a small aperture. Wouldn't any pair of polarized glasses reveal the screen? Also, superspies picking up the monitor's leaky signals would be unaffected by it. Also... seems like he has destroyed a perfectly good monitor (but I guess we have enough).

Inefficient. Rather than making it harder to look at the screen, make viewers not want to look at the screen to begin with. Make the background image goatse. Also provides an interesting location to place the stereotypical "GUI trash can".

Didn't we just spend the last 20 years designing laptop/lcd flatscreens so that they didn't have the damn single-point-of-viewing issue? I seem to recall the original, dim LCD screens being an enormous pain in the butt because if you moved your head about 3" to either side, you couldn't see anything.

With a 3d monitor, it could be interesting to try. For 1 'eye', output the normal image. For the other, output exactly the opposite image. For normal vision, it would look like a solid image, but wearing 1 half of the 3D Glasses should give you the normal image.

I was thinking along the same lines, only using it to make the monitor appear to be showing 'work' on one polarization, and 'play' on the other, so that a passer by sees microsoft word, and you with your glasses see the movie you are actually watching on the other polarization. Not really as easy as all that, but it could be done i suppose.

Wearing polarised sunglasses indoors is kind of obvious. For someone who works with sensitive information, yet is in a publicly accessible area, this is a genuinely great idea.

Hell, I might even suggest this for my own workstation (back to the door, frequently working on sensitive data). I wear glasses anyway; It wouldn't be difficult to fit the film to the lenses I already require.

You and several others who suggested this probably didn't think of two major problems:

1. You're going to be pretty obvious2. You head weighs a LOT. Neck muscles are designed to keep your head straight and turn it, and tilt it for a few moments, mostly into front or back (i.e. getting view of your surroundings, what's right in front of you and above you). Prolonged attempt at even a modest 45 deg sideways tilt will have your neck muscles scream for mercy in just a couple of minutes unless you're very fit - w

Good point, but how long will you be able to do that without alerting your victim? They still need to be high enough to be between your eye and the screen, and close enough to your eyes to give you sufficient view of the screen.

As noted, all methods of "privacy screening" are defeated by an offender willing to spend a significant effort to defeat them. That said, this will defeat all CASUAL people taking a peek, including those who are wearing polarized glasses.

I did a quick test at my desk with my polarized sunglasses and two different monitors. Both blocked the light when I tilted my head 45 degrees to the right and it was at full brightness 45 degrees to the left. The image only was completely blocked in a very narrow range.

I know, I actually exclusively use polarized glasses since I'm something of a swimming enthusiast in the summers (and I learned to hate water reflections), but things like my phone clearly not well visible with glasses on due to polarization issues.

But as I mentioned in another post, try sitting for a while with a 45 degree tilt of your head for more then a few minutes, then report back on just how painful it was for your neck. Not to mention your extreme obviousness to the person you're "spying" on.

This is false. Sunlight is fully unpolarized, therefore it will not be hindered by polarization until it is polarized by being reflected. To quote wikipedia on the origin of usage of polarization in sunglasses:

Some models have polarized lenses, made of Polaroid polarized plastic sheeting, to reduce glare caused by light reflected from polarizing surfaces such as water (see Brewster's angle for how this works) as well as by polarized diffuse sky radiation (skylight). This can be especially useful when fishin

Sunlight is fully unpolarized, therefore it will not be hindered by polarization... polarizing has no effect on brightness of unpolarized light (beyond the impact of filter's imperfect optical properties of course).

A beam of unpolarized light can be thought of as containing a uniform mixture of linear polarizations at all possible angles. Since the average value of cos^2 theta is 1/2, the transmission coefficient becomes I / Io = 1/2.

Unpolarized light from the sun is very uniform in term of linear polarizations

And the transmission coefficient of that unpolarized light - a uniform mixture of linear polarizations - is 50%. You practically just quoted the passage from Wikipedia. I'm not sure if that means you didn't read it, or read it and just didn't understand it.

Actually I quoted from my head, and the last time I studied the subject was a two page lesson from high school physics over a decade ago. I just found the book in question and compared it to your link, and unfortunately it appears to not delve into the intensity issue, which is probably why I was wrong about it.

In my defense, there were multiple false claims in addition to this correct one in those posts, such as claim that polarizing glasses were used to preserve reflections. But that doesn't excuse the fact that I was indeed wrong on this one. Let this be a lesson to all participants: sometimes one proper link and a short explanation of what part of the link explains the problem with the hypothesis goes much further then a lot of saying "because this is how it is".

Looks like my definition of unpolarized light is a bit off. Unpolarized light does not just vibrate along one axis, but my point still remains. The filter will block one whole component of the wave as it passes through, but leave the other untouched.

You are correct that one wavelength will be "stripped" - this is the entire point of the phenomenon we call polarization. Part where your hypothesis falls apart is where you assume that losing one dimension of the wave of light from the Sun reduces the amount of luminance carried by the wave of light from the Sun. This is false.

Part where your hypothesis falls apart is where you assume that losing one dimension of the wave of light from the Sun reduces the amount of luminance carried by the wave of light from the Sun. This is false.

It's not false. It does, and necessarily so. It's the same reason which allows LCD displays to vary between completely dark and completely light. As the angle between the polarization of the light varies with the angle of the filter, the intensity will be reduced by the cosine of that angle.

If you put two polarizing filters in line (with their polarizations aligned to each other), the second filter will not significantly diminish the intensity of the light passing through the first. However, if you rotate t